Production of antimony oxide



M rch 31, 1936'. J. o. BETTERTON PRODUCTION OF ANTIMONY OXIDE I OriginalFiled Jan. 30, 1933 Patented Mar. 31, 1936 UNITED STATES PATENT OFFICE?Signor to American Smelting and Refining Company, New York, N. Y., aCorporation of New Jersey Application January 30, 1933, Serial No.654,'176 Renewed July 10, 1935 10 Claims.

This invention relates to the production of antimony oxide from alloysof antimony and lead, and particularly concerns a new process fortreating such alloys to obtain antimony oxide in a high state o'f purityand possessing an excellent white color tone.

In its broad aspects the invention is an improvement of that describedand claimed by Burt C. Stannard and Calvin W. Haffey in United StatesLetters Patent No. 1,535,743, issued April 28, 1925.

By the present invention white antimony oxide, free from lead or at mostcontaining only insignificant or permissible amounts of that element, isvolatilized directly from antimony-lead alloys having a lead contentwithin the range of appreciable quantities to approximately In general,the invention contemplates establishing an active, thin, molten, mobileslag film, oil-like in appearance, upon the surface of a moltenantimony-lead bath in the presence of a suitable oxidizing atmosphereand so stabilizing the system that practically pure white, lead-freeantimony oxide is volatilized from the Supernatant slag film regardlessof the concentration of lead in the bath within the limits heretoforespecified.

Although the novel features which are believed to be characteristic ofthis invention will be particularly pointed out in the claims appendedhereto, the invention itself, as to its objects and advantages, and themanner in which it may be carried out, may be better understood byreferring to the following description taken in connection with theaccompanying drawing forming a part thereof, in which Fig. 1 is anelevation of one type of apparatus suitable for practising the method ofthe invention; and

Fig. 2 is an elevation taken along the line 2-2 and at right angles tothe elevation of Fig. 1.

Like reference characters denote like parts in the several figures ofthe drawing.

Referring now to the drawing, one suitable form of furnaceassembly isshown c'omprising a steel casing l lined with suitable refractorymaterial 2' with beams 3 supporting a cast-iron melting and fuming pot4. The furnace is mounted on trunnions 5 and may be tilted by suitablemanipula- 'tion of the worm gear 6. A burner 1 opening into heatingchamber 8 is provided for heating the antimony-lead bath 9 in fuming pot4 while flue provides an exit for waste 'combustion gases. A hood lladapted to fitsnugly over'fuming pot 4 is' provided with adjstable`v`entilators z and' an inner cylinder l3. The cylinder [3 is capable ofadjustment both in respect to hood l l and the surface of the bath 9 bysuitable means (not shown) attached to chains 14. A fiue !5 leads fromhood ll to suitable fume recovery apparatus (not shown).

Employing the above-described apparatus, the process may be practiced asfollows: the furnace is brought to the upright position and suitableantimony-hearing material, for example, anti-'- mony dross containingover 40% antimony and the balance substantially lead, charged to the pot4. The metal may be melted and brought to a suitable temperature by heatderived from burner l and any dross formed during the melting downoperation removed from the molten bath. Hood H may then be lowered overthe furning pot and the inner cylinder l3 adjusted so that the loweredge is a suitable distance, for instance, approximately nine inches,above the surface of the bath and the desired distance may be maintainedby suitable readjustment as the metal level falls during the operationof the process due to depletion of the antimony content of the bath byvolatilization of antimony oxide.

Upon removal of the melting-down dross and exposure of the clean moltenmetal to the atmosphere,'a very thin, oil-like, mobile slag film formson the surface of the bath 9 and antimony oxide, white in color andpractically free from lead, rapidly volatilizes. As a thin hard crustappears on the slag film after a time which will depress thevolatilization of antimony oxide if the crust is allowed to accumulate,the slag film is gently worked from time to time, for example, by aniron tool, in order to maintain the thin, molten, mobile slag film andto prevent and break up crust formation, When necessary, the surfaceshould be skimmed with a perforated iron skimming tool or other suitabledevice to remove accumulated crust from the system. The metal should bemaintained -within a controlled temperature range, for instance,approximately 1375 F. to 1500 F., and air admitted in required andregulated Volume through vents l2 in hood Il, care being taken toprevent rupturing the surface of the slag film or' appreciable coolingthereof by the incoming air.

By thus maintaining conditions of equilibrium between the molten bath,the thin slag film and the oxidizing atmosphere, fuming of practicallypure antimony oxide may be efiected until the antimony content of thebath is depleted to approximately 40% antimony. The fume as it arisesfrom the kettle may be conducted out through the inner cylinder !3 ofhood ll to suitable recovery apparatus, for example, a baghouse, a fan(not shown) preferably being utilized in this operation.

When the fuming operation is completed, for example, when the antimonycontent of the bath falls below 40%, the heat may be turned ofi, theburner moved out of the way, the hood raised and the kettle emptied bysuitably Operating the worm gear to tilt the furnace. Thereafter thefu'nace may be brought back to its original position, additionalantimony-hearing material charged to the pot 4 and. the operationrepeated.

It is to be clearly understood that the preceding specific example isgiven merely for purposes of illustration and is in no sense to beconstrued as limiting the broad scope of the invention.

In practising the invention various sources of antimony may be employed.For example, antimony-lead alloys, drosses or materials of similarcomposition containing approximately 40% oimore of antimony are suitablefor the production of antimony oxide by the improved process, althoughan antimony content of 15% or more is preerred. The antimony content ofantimonial lead compositions containing less than 40% antimony may beincreased by adding bars of antimony metal thereto. Also, the source ofantimony may contain ordinary impurities, such as arsenic, tin, copper,sulphur, nickel, bismuth, iron, etc. without special limitation exceptas follows: tin, if present to the extent of more than a few tenthspercent, seriously retards the volatilization of the `antimony until ithas oxidized and is removed by skimming the slag. Hence, tinfree basemetal is preferred. Arsenic, while not affecting the color of theantimony oxide produced, will oxidize and volatilize as arsenious oxidealong with the antimony oxide and, therefore, should not be present if aStrictly arsem'c-free antimony oxide is desired. Non-Volatileimpurities, such ,as copper, bismuth, nickel, iron, etc. have little ifany detrimental efiect and may be present in considerable amounts.Sulphur, if present, is easily oxidized and volatilized as sulphurdioxide gas or remains in the slag as sulphates.

Temperatura control is important if antimony oxide of the desired purityis to be obtained. It has been found that temperatures of 1425 F, to1450 F. are preferable from an Operating standpoint, although thedesired product may be obtained within a temperature range ofapproximately 1375 F. to approximately 1500 F. However, if thetemperature is materially lowered below 1375 F. the thin, active slagfilm becomes less fluid and decreased volatilization results. On theother hand, when the Operating temperature is substantially increasedabove 1500 F., the color of the antimony oxide is detrimentally afiectedwithin a very short time. If, however, the temperature does fallmaterially below 1375 'F., the fiuidity may be promptly restored bydecreasing the Volume of air coming in contact with the film surface andby frequent gentle working of the slag film to break up any crustformation.

As has .already been pointed out, suitable means must be employed togently work the slag film and prevent and/or remove crust formation andthus impart stability to the system. This is important because theformation of any considerable quantity of crust results in lead beingvolatilized which imparts a yellowish or brownish tinge to the fume.This is true even though the volatilization of antimony oxide may notappear to be visibly diminished. Due care should be exercised both inworking the slag film and in admitting air into contact with the surfacethereof in order not to rupture the slag film and thereby efiectvolatilization of lead.

It is also important to note that the moving atmosphere in contact withthe slag film should always be of an oxidizng character, as a reducingatmosphere destroys the film and allows lead to contaminate the antimonyoxide. Also, the oxdizing atmosphere must be of uniform composition andfree from contaminants which would, if present, discolor the volatilizedoxide. Hence, air is preferably used although other oxid'zing gaseswhich will meet the requirements specified may be utilized.

It will thus be appreciated that the present invention makes possiblethe volatilization of pure, white antimony oxide from alloys of antimonyand lead, which phenomenon is remarkable in view of the large amount oflead which may be contained in the molten bath.

By reason of its high purity, antimony oxide produced in accordance withthe principles of the present invention may be utilized in variousindustries demanding antimony oxide possessing a high quality, whitecolor tone. Among other uses, it is particularly adapted for use as apigment in white paints and as an opacifying agent in the enameling art.

The following explanation and Chemical equations are believed toexplain, in part at least, the phenomenal volatilization of pure, whiteantimony oxide, from antimony alloys containing substantial amounts oflead, in accordance with the principles of the present invention. Thisexplanation, however, is advanced merely as a hypothesis and is not tobe considered as binding upon the applicant or in any way affecting thevalidity of the invention.

Vhen the thin slag film first forms on the molten metal, it is believedthat the following two simple Chemical reactions take place:

and that probably the respective amounts of PbO and Sb203 in the slagfilm bear a definite relationship to the ratio of lead to antimony inthe metal bath.

As the moving oxidizing atmosphere comes in contact with this slag filmand enter into reaction therewith, oxidation probably results asfollows:

It would appear that the thin, fluid slag film is highly active as anoxygen carrier due to rapid convection currents therein, thus providingeffective contact between the oxidized lead and antimony compounds andthe antimony in the bath, which results in converting the latter' toantimony oxide which volatilizes.

If the hypothesis and the explanations advanced are correct, there isprobably little lead oxide existing as such in the active slag film bythe time conditions of stabilization and equilbrium are establishedbetween the molten bath, the slag film and the moving oxidizingatmosphere. It appears probable that antimony oxide is rapidly enteringthe slag film, but under normal conditions of operation, it does notaccumulate but is eliminated from the system practically as fast as itis formed.

While certain novel features of the invention have been disclosed andare pointed out in the annexed claims, it will be understood thatvarious omissions, substitutions and changes may be made by thoseskilled in the art without departing from the spirit of the invention.

What is claimed is:

1. The process for treating antimony lead alloys containing less than60% of the latter element which comprises forming a molten bath of suchan alloy within a temperature range of approximately 1375 F. to 1500 F.,introducing a moving oxidizing atmosphere into contact with the surfaceof said bath whereby pure, white antimony oxide is volatilized andgently working the surface of the bath at intervals to maintainstability of the system.

2. The process for treating lead-antimony alloys containing more than40% of the latter element which consists in heating a bath of such analloy to a temperature of approximately 1375 F. to approximately 1500 F.and gently sweeping the surface of the bath with air therebyvolatilizing antimony oxide of high grade both as to purity andwhiteness of color.

3. The process for treating antimony lead alloys containing less than60% of the latter element which comprises forming a molten bath of suchan alloy within a temperature range of approximately 1375 F. to 1500 F.,introducing a moving oxidizing atmosphere into contact with the surfaceof said bath whereby pure, white antimony oxide is volatilized from athin, fluid, mobile slag film covering the surface of the molten bath,gently working said slag film without rupturing same thereby stabilizingthe volatilization of antimony oxide and recovering the volatilizedantimony oxide.

4. The method of directly volatilizing white antimony oxide from anantimony-lead alloy containing more than 40% of antimony which comprisesestablishing and maintaining, within an approximate temperature range of1375 F. to 1500 F., a thin, fluid slag film upon the surface of a moltenbath of such alloy in the presence of a moving oxidizing atmosphere.

5. The method of directly volatilizing white antimony oxide from anantimony-lead alloy containing more than 40% of antimony which comprisesestablishing and maintaim'ng, within a temperature range of 1425 F. to1450 F., a thin, fluid slag film upon the surface of a molten bath ofsuch alloy in the presence of a moving oxidizing atmosphere.

6. In the direct volatilization of antimony oxide from a bath composedsubstantially of lead and antimony, the latter forming more than 40% ofthe total weight of the bath, the improvement which comprises gentlysweeping the bath with air and periodically breaking the crust formed onthe surface of the bath during the volatilization operation.

7. In the direct volatilization 'of antimony oxide from a bath composedsubstantially of lead and antimony, the latter forming more than 40% ofthe total weight of the bath, the improvement which comprises gentlysweeping the bath with air and periodically skimming the crust formed onthe surface of the bath during the volatilization operation.

8. The process of extracting substantially pure,

white antimony oxide from antimony contaminated with lead, whichcomprises maintaining a molten bath of the impure metal at a temperaturesufficient to form and maintain a thin, fluid film on the surface of thebath, subjecting said filmcovered surface to the action of a gaseousoxidizing agent in predetermined Volume without rupturing the filmthereby volatilizing the antimony as antimony oxide without volatilizingthe lead in appreciable amount and recovering the volatilized antimonyoxide.

9. The process of extracting antimony oxide from molten antimonycontaminated with Volatile impurities, such as lead which consists informing a thin, fluid, mobile film on the surface of the molten metal,subjecting said film at an appropriate temperature to the action of acontrolled moving stream of air and maintaining conditions ofequilibrium between the molten metal, film and stream of air by gentlyworking the film at intervals and periodically breaking the crust formedthereon whereby antimony is withdrawn from the bath and substantiallypure antimony oxide is continuously Volatilized from the film.

10. The process for preparing pure, white antimony oxide which comprisesestablishing an active, fluid, mobile slag film on the surface of amolten bath of a lead alloy containing in excess of 40% antimony andcontacting the slag film with a moving, oxidizing atmosphere withoutrupturing said film thereby volatilizing' pure, white antimony oxide.

JESSE OATMAN BETTERTON.

